Coal cleaning



Jan. 17, 192s. C. R. DCWNS ET AL COAL CLEANING Filed May 8, 1925 RN ddor wzmumun NN :osoNNv Nw@ w Patented Jan. 17, i928.` i

f UNITED STATES PATENT OFFICE.

CHARLES R. -DO\VNS. OF NEW HAVEN, CONNECTICUT, AND CHARLES H. STRANGE, OF POTTSVILLE, PENNSYLVANIA, ASSIGNORS T0 HIRSCH-LEDERER SYNDICATE, INC., OF NEW YORK, N. Y., A CORPORATION OF DELAWARE.

con. CLEANING.

i Application led May 8,

Our invention relates to coal cleaning. In order to remove slate and other impurities vfrom coal as it comes from the mine, 1t has been suggested to screen out ythe silt and then subject the mixture of coal, slateet c., to a gravity separation. For this purpose a fluid/mass having a specific gravity intermediate the specific gravity of the coal 'and the specific gravity of the impurities, is used and the mixture supplied thereto whereupon the coal rises and floats near the top of the fluid mass and the heavier impurities sink in the same. Inorder to provide such a fiuid mass, a mixture of water and sand has been suggested, the proportions of water and sand being so adjusted as to bring the specific gravity of the liuid lnassto a value between that of the specific gravity of the coal and that of the specific gravityof the `slate or other impurities. Thel fluid mass is kept in agitation in order'that the specific gravity of the same may remain substantially uniform throughout the entire mass. The use of a dissolved soluble material to produce a fluid of suliiciently high specific gravity to float the coal and allow impurities such as=s1ate to sink has been suggested, but has'not proved commercially successful, and a fiuid mass comprising a mixture of sand in water has proved the more advantageous. In such method the coal is drawn Off at the top of the fluid mass with more or less of the water and sand, while theF slate is ,drawn out separately from the bottom of the Huid mass also with considerable water and sand. Therefore, fresh sand and water must be continuously supplied in order to keep the volume and specific gravity of the fluid mass up to the necessary amount. The slate or similar impurities which arev drawn off ofrom the body of the fiuid mass with considerable sand and water are separated therefrom by washing screens and the sand returned to the cycle. `Also the coal which is drawn off from the top of the fluid mass with more or less of the sand and water, is separated therefrom by washing screens andt esand returned to `the' cycle. In the coal to begin with, thereA is considerable finely dividedcoal or coal dust and also a certain amount of degradation ofthe coal takes place during the *process which thus produces some finely divided coal, which is too neto be sepa- 'tial amount thereof are separated from the 1925. serial No. 28,776.

rated Vfrom the sand on the screens and passes through the screens with the sand. Therefore, this finely divided coal or coal dust 1s returned tothe fluid mass along with the sand. As the proportion of fine coal'or coal dust in the fluid mass thus increases, a condition is reached where the specific grav- 1ty 'of the fiuid mass (due to the accumulation of fine coal therein of relatively low specific gravity) is reduced to a point so that the fluid mass no longerefiiciently floats the '3:7 coal 1n order to separate it from the slate and similar impurities. Therefore it", has been the, practice 1* at short intervals and afterV thefiuid mass has thus become degraded by the inclusion of fine coal, to allow the fluid mass containing sandl and finely divided coal to run to waste and introduce fresh clean sand to form the ,fiuid mass in order to maintain the /p Aer specific gravity of the fluid mass.

The cost of such sand replacement is a very important matter especially with coal which tends to form an appreciable amount of dust and also the finely divided coal or coal dust is lost. A similar loss of value s also takes place even if other materials or other liquids are used to produce the fluid mass.

The main object of our invention is to substantially avoid these'losses and thus render the process less expensive and more efficient. And for this purpose the finely divided coal or the coal dust or a substansand or the like which fiows 4out from the n: fluid mass and after such separation the purified sand is returned to the fluid mass while the separated coal dust is obtained as a valuable byroduct.

Further an more specific objects, features vand advantages w11l more clearly appear from the detail description given below taken in connection with the accompanying drawings which form apart of this specification. In the drawings, Fig. 1 is a diagram illustrating a systemv for carrying out our improvements in one form thereof and Fig. 2 is a digramm'atic detail illustrating a modification. Referringto Fig. l,r the run of mine coal is run from chute 1 onto a screen 2 in order to separate the silttherefrom, the silt falling into a hopper 3 while the remaining coal cific gravity that the coal will float in or at the top thereof while the slate or other heavy impurities sink to the bottom and the gate valve 8 being open, these impurities with considerable sand and water fall into the trap 9. The coal which floats in or at the top of the separator flows off through a trough 10 and on to separating screens 11, 12 and 13 which classify the coal according to size and from the screens 11, 12 and 13, the classified coal is removed by chutes 14,- 15 and 16 respectively. The sand and water and also the fine coal dust or finely divided coal which is too small to `be retained by the screens, passes therethrough mg apparatus 28. This Vinto the hopper 17.

Periodica y the gate valve 8 is closed and the gate va' e 18 at the bottom of the trap 9 is opened perniittin the charge of slate, etc. sand and water in t e trap 9 to be deposited on a separating screen 19 which permits the sand and water to asis therethrough into hopper'20 while the s ate and'similar impurities are removed on chute 21. The sand and water so separated is deposited in the settling tank 22 in whichthefsand settles to the bottom and the excess water flows off through .overflow 23.' This sand which now contains very little impurities is pumped back by centrifugal pump 24 through pipe 25 and returned to the fluid mass in the separator 5 andA also fresh-water is introduced into the fluid mass in separator 5 throughv pipe 26 in order that the volume of the fluid mass in the separator 5 may be ke t at the desired height so that the coal wil run off through "the trough 10. The amount of water introduced through pipe 26 and the amount of sand introduced through pipe 25 is sofregulated as to keep the Vgravity of the fluid5 mass at the desired value. I e

The sand and water containing less 'finely divided coal, from the more or ns 11,

412, 13 is led from the hopper '17 through pipe 27 to the bottom of a otation separatapplaratus 28 may be of any suitable or well own kind, op`

. erating in anyisuitable or well known m'anner to separate the finely dividedcoal from 4 'the sand which is preferably eected` with the aid of a froth flotation agent, i. e. bythe `-use of a relatively small quantityof oil or- 00.

fret-hin agent as distinguished from the use of a re atively large quantityof oil, which latter method is commonly known in the art `as bulk oil flotation, while thev former method using a relatively small quantity of oil or other flotation agent is commonly carried out.

known as l froth flotation. However the bulk oil flotation may be found advantageous in certain cases. .The frothing agent may be introduced at the bottom Y ofthe apparatus 28 and also air under ressure may be introduced at the` bottom o the apparatus in order to aid. in the separation. Likewise other chemicals may be introduced `to aid in the separation. In Fig. 1 the a paratus is shown with an agitator 31 in t e lower part thereof whereby the mass isa tated lin the bottom part of the cell, but su1t.

The purified sand with Water is removed.

from the bottom of the apparatus in any suitable or well known manner and delivered to the settling tank 22 by pipe 33.

From the above it will be seen that not only is the'sand which isdrawn off with the slate etc., Asaved and returned to the process, but 00 i also the sand which is drawn off with the y coal is saved and purified before it is returned to the fluid 1 mass inthe separator .5 f

whereby the fluid mass in the separator 5 1s kept'su'fficiently free from finely ivided coal so that its specific gravity-is kept up to the necessary point, all of which not only results in a substantial saving of sand, but also in a saving -of substantial quantities of fuel values in respectpf the finely divided coal which is obtained from the y froth flotation apparatus .28. v

'a Witlrregard to the sand and water' which ,falls through the. screens 11, 12 and 13, webelieve that most of the finely divided coal is found atthe right hand end of the hopper' 17 ,as viewed in Fig. 1 while the sand and water which come throu h the screen 13 at the opposite or left han end thereof is relatively free from finel divided coal or coal dust.' Therefore this atter portion may need nourther purification. And in order to avoid the waste of energy etc. in purifying such sand, the arrangement shown in-Flg. l2 may be used wherein the hopper 17 only extends under theright-hand end of the screen `13 where it collects substantially all of the sand and water which is polluted with coal dust and delivers same to the froth flotation apparatus 28 by pipe 27. A separate hopper -35 is .provided to receive the relatively ure a sand and water from the opposite end o the screen 13 and this maybe delivered directly to the .settling tankA 22 by means of pipe 36.

In order that the invention may be more clear to those skilled inthe art, we will give a specific example ofthe method as actually Run Aof mine of anthracite coal was passed over wet screens and then assed into the separator containing the lui mass of sand land water having a specific gravity of about1.7. The specific gravity of the fresh sand was 2.6. As the operation continued, portions ofthe fine material from the coal dev-sanding screens l1, 12 and 13 were continuously withdrawn as through the hopper 17 and pipe 27. This was found to be composed of abou't41 $2. of combustible matter and possessed a specific gravity of 2.0. This was treated by the froth flotation step. For this purpose a suspension of one part of the fine coal-sand mixture' and four parts of water was treated in the froth flotation apparatus with about 2% of petroleum fuel Yoil under the combined effect of mechanical agitation and finely divided air bubbles. A clean sand was obtained therefrom containing only 7 .5% of combustible material and having a specific gravity of which was returned to the fluid mass. As a by-product a tine coal was obtained from the top of the flotation apparatus containing only about 17% of ash.y The fine coal paiticles are floated to the surface of thewater in the flotation apparatus in a froth and the frothf is remove( in a manner well understood by those skilled in the art. Various selective agents may be used in the flotation apparatus such as insoluble collectors and soluble frothing agents. Modifying agents such as organic compounds, acids. alkalis and salts may also be used to favorably affect the surfacesof the particles in order that the finel divided coal will be more effectively pre erentially floated from the sand to a point where the latter is suitable for re-use in producing the fluid mass in the separator 5.

The air may be Supplied to the flotation apparatus under pressure or mav be beaten in by the action of agitators. We have found-v that a combination of air under pressure and mechanical@ agitation gives very good results. The flotation step .may be carried out under atmospheric pressure or under increased or diminished ressures. Instead of treating the finely divided coal and sand mixture from the screens 11, 12 and 13, substantial advantage may still be obtained by t permitting the finely divided coal'and sand mixture to be returned to the separation vessel 5 and withdrawing the fine cdal'sand mixture from other parts of the .gravity separation step in the separator 5, purifying the sand so withdrawn and then returning the same to the separator 5. It is not necessary to remove all of the finely divided coal from the sand. at least in `most cases.- Tlie degree of purity of the material re-4 covered to form the fluid mass will begoverned by the special conditions controlling the coal washing in various cases. The invention may be applied to the treatment of agreat variety of coals and also for the separation therefrom of many other impurities and slate. It may be applied to the While we prefer to use for the fluid mass for the gravity separation, a mixture of sand and water, nevertheless many other finely divided materials may be used including clay, finely divided metals, ores, ete. Also while we have mentioned the use of screens such 'as at 19 for separating slate from the sand and water and screens such as ll, 12 and 13 for separating the sized coal from the sand and water, nevertheless, any other suitableseparating or classifying apparatus or devices may be used for these purposes. Before introducing the `coal at 1 it may be subjected to the action of a plurality of screens, one passing all coal including pea size and smaller and the next one passing only the silt. The coal above pea size may go directly to the separator 5,' and likewise one half the coal held on the silt removing screen. The other half of the latter may be mixed, without cleaning, with the discharge from the separator at 10. If desired soluble material may be dissolved in the, water in. or supplied to the separator 5 y to aid in increasing: the specific gravity thereof. If too much water is returned to the' floatation apparatus through pipe 27,'4

a settling tank may be introduced to remove part of the water before the material is introduced into the flotation apparatus.

Also if the amount of water is insufficient more water may be added to pi e-27. Likewise any other suitable vform o flotation apparatus may be used, and'other forms of ap- .paratus may be substituted for the screen 2 or" the same omitted altogether and many other changes and modifications may be made and theinvention embodied in widely by gravity in a liquid having a finely divided solid in suspension therein forming a liquid medium of a specific gravity between that of the coal and impurities, withdrawing ioe finely"divided solid from the gravity separation and treating it by flotation to remove finely `divided coal or otherimpurities which may have collected therein and returning ration of coal from impurities.

2. The process of cleaning `coal which consists in separating therefrom impurities the cleaned solid for further gravity sepa-, a

it has beecome contaminated with substantial amounts/of fine coal, treating said con-` taminated solid. by flotation to remove fine coal therefrom, and returning the cleaned solid to the gravity separation stepv of the A process.

The process of cleaning coal which consistsin separating therefrom impurities of higher specific gravity than the coal, by gravity in a fluid mass having a specific gravity between that of the coal and impurities, the fluid mass comprising water carrying sand in suspension, withdrawing sand from said gravity separation step after it has become contaminated with substantial amounts of fine coal, treating said contaminated sand by froth flotation to remove fine coal-1; therefrom, and returning the cleaned sand to the gravity separation step of the recess.

4. T e process of prises a gravit separation of coal from imurities of `hig er gravity which consists in ceding said coal into an agitated mixture of a comminuted material and water` composing a fluidmass of such a gravity that cleaning coal which com? the coal will oat in the upper part. of said fluid mass and the impurities will sink to the, lower part of said fluid mass, removing the coal and impurities thus separated vfrom said fluid mass, subjeetin a partat least of Y l said fluid inass to a frot flotation step. to remove fine coal therefrom and returnmg -the cleaned fluid mcass to the gravity separation step of the c'oal cleaning process.

5. The procem of cleaning coal containing impurities of higher-specific gravityythan the coul, which consists in feedingthe im ure mass, removing 'impurities from the bottom of the mass, separating purified coalfro'm finely divided solid matter which is removed therewith, and subjecting such finely divided solid matter to flotation separation to separate therefrom .finely divided co'al which is retained therein from said gravity separation. i

In testimony whereof we have signed oui` names to this specification.

cHARLEsR. 'Do CHARLES' H. s ANGE. 

